Its effects can be similar to those of a cognitive bias, it can even be considered as a subcategory of such biases. The specificity is that the cause lies in one's desires or fears, which divert the attention of the person, more than in one's reasoning.

Neuroscience experiments have shown how emotions and cognition, which are present in different areas of the human brain, interfere between each other in the decision making process, resulting often on a primacy of emotions over reasoning [1]

This might explain some irrational and damaging reactions and moves that might take place when those emotions are biased (in case of over-optimism or over-pessimism for example).